The book says to prove your answers. The proofs can be very informal. Some of those proofs can be done in a single line. If you can't think of even an informal proof, give some sort of reasoning to support your answer.
Let L be the language over the alphabet {a,b,c,+,-,(,),*} consisting of algebraic expressions where variables have one-letter names, and where the minus sign always indicates subtraction.
For example, if the input string is a-b-c*(a*c-b-(a-b)) then the output string should be ab-cac*b-ab--*